1. Field of the Invention
The present invention relates to a flexible multilayer substrate.
2. Description of the Related Art
A substrate referred to as a “flexible multilayer substrate” may be used in some cases in a mobile phone, a digital camera and the like, for example. The flexible multilayer substrate includes at least a flexible portion. The flexible multilayer substrate may also include both a rigid portion and the flexible portion. Such a flexible multilayer substrate including both the rigid portion and the flexible portion is also called a “rigid-flexible multilayer substrate”. The flexible portion of the flexible multilayer substrate is formed by stacking one or more soft insulating layers. A resin layer is used as the soft insulating layer.
The flexible multilayer substrate is used in some cases in a portion where bending occurs within some kind of device in use. The flexible multilayer substrate is also used in some cases in a portion that needs to be bent and attached during assembly, even if the portion is immobile in use.
A conductor pattern such as a wiring is arranged in some cases inside the flexible portion of the flexible multilayer substrate. One example of the flexible multilayer substrate is disclosed in Japanese Patent Laying-Open No. 8-330683. The flexible multilayer substrate disclosed in this document is a rigid-flexible multilayer substrate. In the example disclosed in this document, the flexible portion is formed by a film made of polyimide. Inside the flexible portion as well, a conductor pattern, i.e., a copper foil pattern, serving as the wiring is laid. The conductor pattern is normally formed by a metal pattern. The flexible portion may be formed by arranging the metal pattern on a surface of a resin layer and stacking one or more resin layers.
In recent years, it has been desired to increase the number of conductor patterns arranged in the flexible portion of the flexible multilayer substrate. However, the flexible portion is a portion that is bent in use, and the resin layer itself and the conductor pattern are different in bendability. Therefore, if too many conductor patterns are provided inside the flexible portion, the conductor patterns may come into contact with each other and short circuit may occur when the flexible portion is bent.